1. Field of the Invention
The present invention relates to a keyboard entry circuitry for determining accurately which one of a plurality of input keys is actuated, and more particualarly to keyboard entry circuitry effective to shorten the period of time required for determinations as to the actuation of a specific key of a keyboard.
2. History of the Prior Art
Keyboard entry circuitry for calculator purposes is conventionally of the key strobing type. This conventional key strobing type of the keyboard entry system utilizes key strobing digit time signals of only one kind supplied to the respective keys of a keyboard and digit time signals outputted via a specific actuated key are sampled several times. Subsequent to this, that keyed information is transferred to a data receiving circuitry. The repetition of sampling is to avoid errors in the key determinations which will be caused due to noises.
That is, when a specific key is actuated, a sampling counter is loaded with the count required for sampling. First of all, determinations are effected as to whether a specific key is actuated and, if an affirmative answer is given, determinations are then effected as to whether the contents of the sampling counter are "0". If the sampling counter is not "0", it will be decremented by one and the operation will be returned to determinations as to the presence or absence of any actuated key. the above operations are sequenced in this manner. Unless "0"is reached by the count of the sampling counter, the identify of the keyed information is not provided.
The count of the sampling cycles is properly chosen due to noise occurrence states and period of time for key actuation. However, because the sampling procedures are repeated several times to confirm an equivalency of the keyed information thereby to avoid errors in key entry, a period of the sampling procedures becomes substantially longer with an accompanying longer period of time up to completion of arithmetic operations on the keyed information.